#include <bits/stdc++.h>
using namespace std;

#define all(x) begin(x), end(x)
#ifdef CKISEKI
#define safe cerr << __PRETTY_FUNCTION__ << " line " << __LINE__ << " safe\n"
#define debug(a...) debug_(#a, a)
#define orange(a...) orange_(#a, a)
#include <experimental/iterator>
void debug_(auto s, auto ...a) {
  cerr << "\e[1;32m(" << s << ") = (";
  int f = 0;
  (..., (cerr << (f++ ? ", " : "") << a));
  cerr << ")\e[0m\n";
}
void orange_(auto s, auto L, auto R) {
  cerr << "\e[1;33m[ " << s << " ] = [ ";
  using namespace experimental;
  copy(L, R, make_ostream_joiner(cerr, ", "));
  cerr << " ]\e[0m\n";
}
#else
#define safe ((void)0)
#define debug(...) safe
#define orange(...) safe
#endif

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n, k;
  cin >> n >> k;
  vector<array<int, 2>> a(n);
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < 2; ++j)
      cin >> a[i][j];
  }
  sort(a.begin(), a.end());
  do {
    bool ok = true;
    vector<int> c(n);
    for (int x = 1; x <= 100; ++x) {
      for (int j = 0; j < n; ++j)
        c[j] = x == a[j][0] || x == a[j][1];
      int cnt = 0;
      for (int i = 0; i < n; ++i)
        cnt += c[i] == 0 and c[(i + 1) % n] == 1;
      if (cnt >= 2) {
        ok = false;
      }
    }
    if (ok) {
      cout << "possible\n";
      for (int i = 0; i < n; ++i)
        cerr << a[i][0] << ' ' << a[i][1] << '\n';
      return 0;
    }
  } while (next_permutation(a.begin(), a.end()));
  cout << "impossible\n";
  return 0;
}